The present invention concerns a method for making devices, particularly devices having an intermetallic structure that are useful for small energy and chemical systems, and devices made by the method.
Microtechnology-based Energy and Chemical Systems (MECS) are devices that rely on embedded microstructures for their function. MECS devices are mesoscopic, i.e. in a size range between macro objects, such as automobile engines and laboratory vacuum pumps, and the intricate Microtechnology-based ElectroMechanical Systems (MEMS) sensors that reside on a chip. Mesoscopic systems are expected to perform a number of important functions where a premium is placed on mobility, compactness, and/or point application. Internal processes of MECS devices operate on dimensional scales that are much smaller than traditional systems. For thermal and chemical applications, a small characteristic size provides the benefits of high rates of heat and mass transfer, large surface-to-volume ratios, and the opportunity for operating at elevated pressures.
One subclass of MECS devices that is of great interest, both for research and industrial applications, comprises high-temperature microreactors and micro-scale heat exchangers. Potential applications for microreactors include: portable power packs that may extend the operating times of devices by a factor of ten or more; on-site neutralization of toxic chemicals, eliminating the need for transport and burial; miniaturized bioreactors that can enhance production of therapeutic drugs, or others that can detect toxic compounds; gasification of coals and heavy oils; flue gas desulphurisation, and incineration of hazardous materials. Potential applications for micro-scale heat exchangers include: heat recovery for recycling waste heat; steam superheating for driving turbines; and recuperators for jet engines and diesel engines. These and other potential applications are discussed in U.S. patent application Ser. No. 09/369,679, xe2x80x9cMicrolamination Method for Making Devices,xe2x80x9d and U.S. patent application Ser. No. 60/095,605, xe2x80x9cMethods for Making Devices by Component Dissociation and Microprojection Welding,xe2x80x9d which applications are incorporated herein by reference. Other features and applications pertinent to the present invention also are described in Paul, B. K., T. Dewey, D. Alman and R. D. Wilson, xe2x80x9cIntermetallic Microlamination for High-Temperature Reactors,xe2x80x9d 4th Int. Conf. Microreaction Tech., Atlanta, Ga., Mar. 5-9, 2000, pp. 236-243 (American Institute of Chemical Engineers [AIChE]) incorporated herein by reference.
Because of the stringent operating requirements for microreactors, previous microreactors have been constructed using materials such as stainless steel. The work of D. W. Matson et al., xe2x80x9cFabrication of Microchannel Chemical Reactors Using a Metal Lamination Process,xe2x80x9d Proc. IMRET3 (April, 1999, Frankfurt Germany), represents one such microreactor constructed of 316 stainless steel; another is the work of V. Hessel et al., xe2x80x9cHigh Temperature HCN Generation in a Complex Integrated Micro-reaction System,xe2x80x9d Proc. IMRET3 (April, 1999, Frankfurt Germany). At elevated temperatures of about 550xc2x0 C. and above, stainless steel has low creep resistance, i.e., a high tendency to deform. The creep resistance of stainless steel is too low to be generally suitable for many high-temperature microreactor applications, such as steam superheating for driving turbines, gasification of coals and heavy oils, flue gas desulphurisation, waste heat recovery, incineration of hazardous materials, mobile engine heat recovery, and hydrogen steam reforming.
Ceramics have been identified as a possible structural material for making microreactors suited to high temperature applications. See, M. Kim et al., xe2x80x9cThe Fabrication of Flow Conduits in Ceramic Tapes and the Measurement of Fluid Flow through These Conduits,xe2x80x9d Proceedings of the ASME Dynamic Systems and Controls Division, DSC V. 66, 1998. Ceramics have a very high melting point, low thermal conductivity and high corrosion resistance. Certain ceramic properties make them unsuitable for such applications. For example, sintered ceramics can sag, then shrink and/or warp during binder removal after the sintering process is complete. Furthermore, sintered ceramics have low fractional densities, which indicates high porosity.
For the applications mentioned above, intermetallics as a class of materials have material properties more desirable than those of the previously discussed materials, such as high melting point, low thermal conductivity, and good corrosion resistance. It would be advantageous to be able to form MECS devices from intermetallics, and thus make use of high-temperature properties of intermetallics. However, to date this has proved virtually impossible because intermetallics are too brittle and therefore are poor substrates for facile machining and forming at room temperature.
Embodiments of a method and apparatus for making an intermetallic device, or a device having at least an intermetallic component, are described. One embodiment of the method comprises making an intermetallic structure from laminae having one or more layers comprising substantially pure metals. Laminae are patterned to provide features, shapes, etc., which collectively define a desired structure, by machining, lithography and etching, or other patterning technology. A lamina can be patterned because at least that portion of the lamina that must be patterned comprises a patternable metal or alloy. In some embodiments, each of the layers of the lamina comprised substantially pure, patternable metal or metal alloys, which are patternable. Patterned, and possibly non-patterned laminae, are then stacked and registered in the order needed to create the final monolithic intermetallic structure. The stack of registered, patterned laminae is then processed to form a monolithic, intermetallic structure.
Patterning lamina or laminae prior to making the intermetallic eliminates the need to pattern intermetallic compounds, which typically are (1) difficult to roll into sheets of the preferred thickness range for micro-reactor applications, and (2) difficult to pattern, as intermetallics tend to be brittle at room temperature.
For those intermetallics capable of being rolled into sheets from, for instance, from directionally solidified intermetallic ingots, and then patterned through means such as lithography and chemical etch, monolithic intermetallic structures can be formed from intermetallic blank layers, particularly homogeneous (single phase composition materials) layers, that have been machined and/or otherwise patterned. The layers are then stacked and registered. The stack is subsequently bonded by a process, such as diffusion bonding, to form a monolithic intermetallic structure. This process may not be feasible for all intermetallics, such as NiAl, because there currently is no method known for rolling such materials to form foils.
Monolithic intermetallic structures may be formed with different internal geometries, topologies and/or topographies, thereby allowing for different applications. Because of their properties, including high melting temperature, high (or low) thermal conductivity (depending on the intermetallic), and high corrosion resistance, intermetallics are excellent candidates for microreactors. Applications include portable fuel cells; chemical detoxification apparatuses for environmental purposes; on-site neutralization of toxic chemicals; miniaturized bioreactors for production of pharmaceuticals; and toxic substance detection apparatuses. In addition, intermetallics are excellent materials for making high-temperature micro-scale heat exchangers.
Monolithic intermetallic structures can contain catalysts that promote specific chemical reactions, such as that needed to produce hydrogen in a fuel cell. Monolithic intermetallic structures may be fabricated so as to contain microscopic internal features, or macroscopic internal features, depending on the application, according to embodiments of the present invention.